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  • Elsevier  (383,576)
  • Krefeld : Geologischer Dienst Nordhein-Westfalen
  • Irkutsk : Ross. Akad. Nauk, Sibirskoe Otd., Inst. Zemnoj Kory
  • 2005-2009  (383,578)
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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 317 (1993), S. 474-484 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
  • 5
    Publication Date: 2017-10-09
    Description: Cosmogenic radionuclides in the one-million-year half-life range offer unique possibilities for age determinations in geophysics. In measurements where the radioactive decay is being utilized as a clock, uncertainties in age determinations may be reduced if the ratio of two radioisotopes with different half-lives can be used as a chronometer. In this work we investigate the atomic ratio of atmospheric 26Al (t1/2= 0.717 Ma) to 10Be (t1/2=1.386 Ma) measured with accelerator mass spectrometry (AMS), and its potential as a chronometer for dating old ice. The 26Al/10Be ratio decreases with an effective half-life of t1/2(26Al/10Be)= 1.49 Ma. For its application as a chronometer, the atmospheric 26Al/10Be ratio has to be well characterized. However, the properties of atmospheric 26Al have been understood only poorly so far. At the VERA AMS facility of the University of Vienna, a first systematic study of the global variations of the 26Al/10Be ratio in the atmosphere and in surface firn has been carried out, and pilot measurements of the 26Al/10Be ratio in deep Antarctic ice have been performed. Our results indicate that this ratio is globally constant to within 5% in the atmosphere and in surface firn with a mean value of 1.89×10−3. The data also suggest that non-atmospheric sources of 26Al, such as extraterrestrial, in situ produced or re-suspended 26Al, do not contribute significantly to the observed 26Al/10Beratio. In addition, atmospheric mixing seems to exert only aminor influence. In a first application of the method,26Al/10Be ratios were measured in chips collected in connection with the drilling of the lowest part of an ice core (2250 to 2760 m) in Dronning Maud Land,Antarctica. Surprisingly, variable 26Al/10Be ratios ranging between0.5 and up to 2 times the atmospheric ratio were found at different locations in this deep ice core. While the cause for the ratios higher than atmospheric remains unexplained so far, the ratios lower than atmospheric may be caused by radioactive decay, allowing a first dating attempt using the 26Al/10Be ratio. Thus, at an ice depthof 2760 m an approximate date of (6.7±2.6)×105years was established.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 (9). pp. 1440-1448.
    Publication Date: 2016-11-01
    Description: The phytoplankton distribution off western Australia in the period from April to October is unique in that high biomass is generally associated with anticyclonic eddies and not with cyclonic eddies. As the western Australian region is oligotrophic this anomalous feature must be related to differing nutrient supply pathways to the surface mixed layer of cyclonic and anticyclonic eddies. A suite of modelled abiotic tracers suggests that cyclonic eddies are predominantly supplied by diapycnal processes that remain relatively weak until June–July, when they rapidly increase because of deepening surface mixed layers, which start to tap into the nutrient-replete waters below the euphotic zone. To the contrary, we find that anticyclonic eddies are predominantly supplied by injection of shelf waters, which carry elevated levels of inorganic nutrients and biomass. These injections start with the formation of the eddies in April–May, continue well into the austral winter and reach as far as several hundred kilometers offshore. The diapycnal supply of nutrients is suppressed in anticyclonic eddies since the injection of warm, low-salinity shelf waters delays the erosion of the density gradient at the base of the mixed layer. Our results are consistent with the observed seasonal cycles of chlorophyll a and observation of particulate organic matter export out of the surface mixed layer of an anticyclonic eddy in the region.
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  • 7
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    Elsevier
    In:  Environmental Modelling & Software, 24 . pp. 1012-1013.
    Publication Date: 2018-09-12
    Description: The presented software application allows GUI-based access to the bubble dissolution model presented by McGinnis et al. [McGinnis, D.F., Greinert, J., Artemov, Y., Beaubien, S.E., Wüest, A., 2006. The fate of rising methane bubbles in stratified waters: what fraction reaches the atmosphere? Journal of Geophysical Research 111, C09007. doi:http://dx.doi.org/10.1029/2005JC003183]. It quantifies the dissolution of gas bubbles (containing any combination of CH4, CO2, O2, N2, and Ar) in marine or lacustrine environments based on the initial bubble size, free gas composition and environmental parameters (temperature, salinity, and dissolved gas concentrations). The software enables scientists and engineers to evaluate bubble dynamics in a simple way on Windows® PCs
    Type: Article , PeerReviewed
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  • 8
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    Elsevier
    In:  Remote Sensing of Environment, 113 (9). pp. 1853-1867.
    Publication Date: 2019-01-23
    Description: A new Bitemporal Mineral Dust Index (BMDI) is derived from Meteosat Second Generation (MSG) infrared observations over land at two different time slots per day. This daily dust index is evaluated with AErosol RObotic NETwork (AERONET) surface observations, MODerate resolution Imaging Spectro-radiometer (MODIS) “Deep Blue” Aerosol Optical Depth (AOD) and Ozone Monitoring Instrument (OMI) Aerosol Index, showing a good capability of the BMDI for dust detection and dust load estimation over land and also over deserts. BMDI dust detection is shown to be limited in scenes with high atmospheric humidity as e.g. coastal regions. In particular the insensitivity of BMDI to biomass burning aerosol is shown, leading to the possibility of remote sensing of mineral dust also in regions with large contributions of biomass burning aerosol to the total column aerosol concentrations. Time series of mineral dust as inferred from BMDI for the year 2006 are presented for four regions over the Sahara. These time series show strong (and different) annual cycles of dust load for all four regions. Especially the strong episodic character of atmospheric dust in the main source regions can be inferred from BMDI observations.
    Type: Article , PeerReviewed
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  • 9
    Publication Date: 2019-09-23
    Description: The Logatchev hydrothermal field (14 degrees 45'N on the MAR) is one of a few submarine hydrothermal systems associated with ultramafic rocks. It is situated on the eastern inner flank of the rift valley wall, 7 km away from the spreading axis and its formation has previously been linked to detachment faulting and core complex formation. Geological mapping during various ROV dives, geological sampling, and shallow drilling reveal a structural control of hydrothermal activity as well as its location in a debris flow consisting of heterogeneous ultramafic and mafic intrusive rocks. The mixed mafic/ultramafic host rock lithology is in agreement with published vent fluid and gas chemical data showing characteristics for interaction with mafic as well as with ultramafic rocks. Massive sulfide formation is more focused than previously thought and likely limited to a thin veneer at the seafloor. The Logatchev hydrothermal field shows a number of peculiarities that are unusual for most other hydrothermal systems. One of these are so-called,smoking craters", seafloor depressions that are several meters wide, characterized by an elevated crater rim made up partly of sulfide talus but also of abundant wall rock material. At these smoking craters hydrothermal venting occurs directly from holes within the craters and from small, cm to dm high, Cu-rich chimneys occurring at the crater rim. Based on geological mapping and sampling we suggest that these smoking craters are the product of processes related to the regional and local geological setting in an ultramafic-hosted, off-axis location with abundant landslides, as well as off-axis gabbroic intrusions providing the heat for the hydrothermal convection cell. (C) 2009 Elsevier B.V. All rights reserved.
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  • 10
    Publication Date: 2019-09-23
    Description: Widespread mud volcanism across the thick (〈= 14 km) seismically active sedimentary prism of the Gulf of Cadiz is driven by tectonic activity along extensive strike-slip faults and thrusts associated with the accommodation of the Africa-Eurasia convergence and building of the Arc of Gibraltar, respectively. An investigation of eleven active sites located on the Moroccan Margin and in deeper waters across the wedge showed that light volatile hydrocarbon gases vented at the mud volcanoes (MVs) have distinct, mainly thermogenic, origins. Gases of higher and lower thermal maturities are mixed at Ginsburg and Mercator MVs on the Moroccan Margin, probably because high maturity gases that are trapped beneath evaporite deposits are transported upwards at the MVs and mixed with shallower, less mature, thermogenic gases during migration. At all other sites except for the westernmost Porto MV, delta C-13-CH4 and delta H-2-CH4 values of similar to -50 parts per thousand and -200 parts per thousand, respectively, suggest a common origin for methane; however, the ratio of CH4/(C2H6 + C3H8) varies from similar to 10 to > 7000 between sites. Mixing of shallow biogenic and deep thermogenic gases cannot account for the observed compositions which instead result mainly from extensive migration of thermogenic gases in the deeply-buried sediments, possibly associated with biodegradation of C2+ homologues and secondary methane production at Captain Arutyunov and Carlos Ribeiro MVs. At the deep-water Bonjardim, Olenin and Carlos Ribeiro MVs, generation of C2+-enriched gases is probably promoted by high heat flux anomalies which have been measured in the western area of the wedge. At Porto MV, gases are highly enriched in CH4 having delta C-13-CH4 similar to -50 parts per thousand, as at most sites, but markedly lower delta H-2-CH4 Values 〈 -250 parts per thousand, suggesting that it is not generated by thermal cracking of n-alkanes but rather that it has a deep Archaeal origin. The presence of petroleum-type hydrocarbons is consistent with a thermogenic origin, and at sites where CH4 is predominant support the suggestion that gases have experienced extensive transport during which they mobilized oil from sediments similar to 2-4 km deep. These fluids then migrate into shallower, thermally immature muds, driving their mobilization and extrusion at the seafloor. At Porto MV, the limited presence of petroleum in mud breccia sediments further supports the hypothesis of a predominantly deep microbial origin of CH4. (C) 2009 Elsevier B.V. All rights reserved.
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  • 11
    Publication Date: 2017-08-08
    Description: Nicaragua comprises seven historically active volcanoes (Cosigüina, San Cristobal, Telica, Cerro Negro, Momotombo, Masaya, and Concepcion), five of which are in a state of continuous degassing. Published measurements of the atmospheric dispersion of continuous emissions from Nicaraguan volcanoes, the chemical and aerosol microphysical modifications of the released gases and aerosols, and related acid deposition and impacts on the environment cover only short periods of time. We applied a three-dimensional atmosphere-chemistry/aerosol numerical model over Central America focussing on Nicaraguan volcanic emissions for month long simulation periods during the dry and wet seasons of 2003. The model is able to reproduce observed monthly precipitation and wind speed throughout the year 2003. Model results for near surface SO2 concentrations and SO2 dry deposition fluxes around Masaya volcano are in very good agreement with field measurements. During the dry season, oxidation of SO2 to sulphate plays only a minor role downwind of the Nicaraguan volcanoes and over the Pacific Ocean, whereas SO2 released from Arenal and Poas in Costa Rica is oxidised to sulphate much faster and closer to the volcanoes due to higher humidity and cloud water availability. During the wet season, more variable wind conditions lead to reduced dispersion of SO2 over the Pacific Ocean and increased dispersion inland. The availability of liquid water in the atmosphere favours sulphate formation close to the Nicaraguan volcanoes via aqueous phase oxidation and represents another limitation for the dispersion of SO2. Strong precipitation removes sulphate quickly from the atmosphere by wet deposition. Atmospheric SO2 concentrations and in particular dry deposition close to the volcanoes show a pronounced diurnal cycle.
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  • 12
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    Elsevier
    In:  Progress in Oceanography, 83 . pp. 143-150.
    Publication Date: 2016-10-04
    Description: The coastal upwelling off Mauritania and its connection with the oxygen minimum zone (OMZ) in the tropical Atlantic is investigated in an eddy-resolving general circulation model. Two main supply routes for the upwelling are identified. First a southern eastward pathway crossing 23 degrees W between 3 degrees N and 10 degrees N related to the equatorial zonal current system supplies up to 50% of the water upwelled in winter, and about 30% in summer. Second, another eastward pathway crossing 23 degrees W further north between 28 degrees N and 38 degrees N supplies 35% of the upwelled water in spring compared to 25% during the rest of the year. Most of the water of the northern pathway is entrained into the mixed layer already before reaching the upwelling region. Only the southern pathway contributes not recently ventilated waters to the upwelling. The connection with the OMZ is very weak, only about 1% of the upwelling waters originate here. On the other hand, if water from the OMZ reaches the surface mixed layer within 6 years, this mostly (71%) happens in the upwelling region
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  • 13
    Publication Date: 2017-09-27
    Description: We critically evaluate the applicability of Ca-isotope ratios in planktonic foraminifers as proxy for past sea surface temperatures (SST) and isotope composition of paleo-seawater (δ44Casw) reconstructions. Previous studies have shown discrepancies regarding the temperature sensitivity of Ca isotope fractionation in foraminifers of more than one order of magnitude. We present new data from the planktonic foraminifer species Orbulina universa, Globigerinoides sacculifer and Neogloboquadrina pachyderma (sinistral) from culture experiments, multinet deployments and coretop samples. Specimens of G. sacculifer cultured at low salinities (33–34.5) show predominantly no major temperature dependent Ca isotope fractionation, in contrast to previous individuals cultured at higher salinities of 34.5–36. The new data of O. universa are consistent with previously published results, revealing a small but significant temperature sensitivity. Calcium isotope fractionation in tests of N. pachyderma shows a significant variation with temperature, which is not uniform over the total investigated temperature range (−1.6 °C to +10 °C), possibly reflecting the influence of additional controlling factors besides temperature. Controlled dissolution experiments in the laboratory indicate that the Ca-isotope composition of G. sacculifer and N. pachyderma is relatively insensitive to partial dissolution of their tests. Calcium isotope ratios in the planktonic foraminifers G. sacculifer and N. pachyderma (s) reveal a complex Ca isotope fractionation behaviour, which is not yet fully understood. Additional validation studies are crucial to enhance the basic understanding of the calcium isotope systematics in planktic foraminifer shells, and the potential for applying Ca-isotope ratios as proxies for seawater temperature and the oceanic Ca budget.
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  • 14
    Publication Date: 2017-08-04
    Description: Studying the morphology and subsurface geometry of mud volcanoes provides insights into their activity. This paper describes the internal structure of the Håkon Mosby mud volcano (HMMV) in the southwestern Barents Sea and presents a conceptual model of its evolution. The lack of a mud edifice and the profuse gas flares suggest that in the recent past the mud volcano evolution was predominantly controlled by venting of gas-rich fluids and free gas. However, the analysis of high-resolution single-channel seismic (SCS) data reveals for the first time the existence of a pseudo-mud chamber at the top of the 3 km deep central conduit. It was once created at the seabed and is now a buried expression that acts as mud chamber. The pseudo-mud chamber is situated approximately 300 m below the seafloor, directly above the 330 ka Bear Island Slide (BIS) scar reflection and below glacigenic debris flow deposits that constitute the sediment on top. The sediment profiler data indicates a younger mud deposit above the debris flows, which points to a reactivation of the mud volcano. The reactivation was most likely triggered by the contrast in density between the gas-rich mud chamber and the high-density debris flow deposits. Three stages, i.e. initiation, sealing and reactivation, and a second active period define the evolution of this young mud volcano. Both, the morphology and size of the conduit as well as in-situ temperature gradients point towards a focused and rapid fluid flow.
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  • 15
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 . pp. 91-101.
    Publication Date: 2017-09-27
    Description: The first Hf isotope data for seawater are reported for a series of stations in the Northwestern Pacific and define a range from epsilon(Hf) = 3.5 +/- 1.4 to 8.6 +/- 1.6. Most samples have values within error of the average of epsilon(Hf) = 5.9, but significant variations are found in intermediate waters at a depth of 600 m, as well as in deep waters. The Nd and Hf isotope compositions of the deep waters fall within the range of values found for surfaces of hydrogenetic ferromanganese crusts in the region, confirming that Hf in the Fe-Mn crusts has been derived from the overlying water column, which thus provide an archive of past seawater compositions. Although the seawater samples are generally close to the global epsilon(Nd)-epsilon(Hf) correlation obtained from ferromanganese crusts, there are significant deviations from this correlation indicating that there is some additional decoupling between Nd and Hf isotope signals, most likely caused by local water mass mixing and differences in residence times. This is not resolved in the crust samples, which integrate seawater signals over 10(4) years. The combined use of these two isotope systems in seawater therefore provides an additional dimension for tracing water masses in the oceans. Studies of the distribution of oceanic Hf isotope compositions that have been confined to deep water and boundary waters, as recorded in seafloor ferromanganese crusts, can now be extended and aimed at characterising the entire present-day water column. Average Hf concentrations measured in this study are somewhat lower than previously reported, suggesting a shorter residence time for Hf in the global oceans, although the uncertainty in the extent of Hf removal from the water column during estuarine mixing as well as a lack of data on hydrothermal and dust inputs remains a limit on how well the residence time can be defined. (C) 2008 Elsevier Ltd. All rights reserved.
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  • 16
    Publication Date: 2019-09-23
    Description: Based on proxy records from western Black Sea cores, we provide a comprehensive study of climate change during the last glacial maximum and late-glacial period in the Black Sea region. For the first time we present a record of relative changes in precipitation for NW Anatolia based on variations in the terrigenous supply expressed as detrital carbonate concentration. The good correspondence between reconstructed rainfall intensity in NW Anatolia and past western Mediterranean sea surface temperatures (SSTs) implies that during the glacial period the precipitation variability was controlled, like today, by Mediterranean cyclonic disturbances. Periods of reduced precipitation correlate well with low SSTs in the Mediterranean related to Heinrich events H1 and H2. Stable oxygen isotopes and lithological and mineralogical data point to a significant modification in the dominant freshwater/sediment source concomitant to the meltwater inflow after 16.4 cal ka BP. This change implies intensification of the northern sediment source and, with other records from the Mediterranean region, consistently suggests a reorganization of the atmospheric circulation pattern affecting the hydrology of the European continent. The early deglacial northward retreat of both atmospheric and oceanic polar fronts was responsible for the warming in the Mediterranean region, leading simultaneously to more humid conditions in central and northern Europe.
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  • 17
    Publication Date: 2017-09-27
    Description: We present major and trace element and Sr–Nd–Pb and U–Th–Pa–Ra isotope data for a small sample suite of primarily post-glacial, mildly alkalic volcanic rocks from the Snaefellsjökull central volcano situated off the main rift systems in western Iceland. The volcanic rocks are crystal-poor and range from olivine alkali basalt to trachyte and show tight correlations of major and trace elements that are explained by fractional crystallization involving removal of olivine, plagioclase, clinopyroxene, Fe–Ti oxide and apatite. Sr–Nd–Pb isotopes are practically invariant, consistent with derivation from the same source region. During fractionation from primitive basalt to evolved trachyte, (230Th/232Th), (230Th/238U) and (231Pa/235U) decrease progressively at broadly constant (238U/232Th). A continuous closed-system fractionation model that assumes constant initial (230Th/232Th) in the basaltic precursor melt indicates that hawaiite was derived from olivine basalt by not, vert, similar50% fractional crystallization within View the MathML source and trachyte by not, vert, similar80% fractionation within View the MathML source. An overrepresentation of evolved basalts and hawaiites with young inferred magma ages in the dataset is consistent with the parental precursor to these magmas intruded into the sub-volcanic magma plumbing system as a consequence of lithospheric rebound caused by deglaciation. Lavas affected by apatite removal have higher (231Pa/235U) than predicted for simple radioactive decay, suggesting apatite significantly fractionates U from Pa. The proposed fractionation model consistently explains our U-series data assuming View the MathML source and View the MathML source and View the MathML source. If applicable, these D values would indicate that the effect of apatite fractionation must be adequately considered when assessing differentiation time scales using (231Pa/235U) disequilibria data.
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  • 18
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    Elsevier
    In:  Ocean Modelling, 27 . pp. 98-106.
    Publication Date: 2019-09-23
    Description: Combining the buoyancy and tracer budget in the generalised Temporal Residual Mean (TRM-G) framework of [Eden, C., Greatbatch, R.J., Olbers, D. 2007a. Interpreting eddy fluxes. J. Phys. Oceanogr. 37, 1282–1296], we show that within the small slope approximation and weakly diabatic situation, the isopycnal diffusivity is related to the difference of the streamfunctions of the eddy-induced velocities of tracer and buoyancy divided by the angle between the (negative) slopes of isopycnals and the isolines of the tracer. Using this result tracer simulations of a realistic mesoscale-eddy-permitting model of the North Atlantic coupled to a biogeochemical model are diagnosed in terms of zonal (View the MathML sourceKI(x)) and meridional (View the MathML sourceKI(y)) isopycnal diffusivities relevant for non-eddy-permitting ocean models. We find for tracers having different interior sources and surface forcing and therefore different lateral and vertical mean gradients, values of View the MathML sourceKI(x) and View the MathML sourceKI(y) with similar magnitudes and lateral and vertical structure. In general, isopycnal diffusivities lie within the expected range between 0 and 5000 m2/s but we also find a strong anisotropy with View the MathML sourceKI(x) much larger than View the MathML sourceKI(y) over large regions of the North Atlantic. Both View the MathML sourceKI(x) and View the MathML sourceKI(y) are larger within and above the thermocline but decay almost to zero below. Our results also support the common practise of the use of identical isopycnal and thickness diffusivity for any tracer in ocean models.
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  • 19
    Publication Date: 2019-09-23
    Description: The mechanisms driving the air–sea exchange of carbon dioxide (CO2CO2) in the North Sea are investigated using the three-dimensional coupled physical–biogeochemical model ECOHAM (ECOlogical-model, HAMburg). We validate our simulations using field data for the years 2001–2002 and identify the controls of the air–sea CO2CO2 flux for two locations representative for the North Sea's biogeochemical provinces. In the seasonally stratified northern region, net CO2CO2 uptake is high (View the MathML source2.06molm-2a-1) due to high net community production (NCP) in the surface water. Overflow production releasing semi-labile dissolved organic carbon needs to be considered for a realistic simulation of the low dissolved inorganic carbon (DIC) concentrations observed during summer. This biologically driven carbon drawdown outcompetes the temperature-driven rise in CO2CO2 partial pressure (pCO2pCO2) during the productive season. In contrast, the permanently mixed southern region is a weak net CO2CO2 source (View the MathML source0.78molm-2a-1). NCP is generally low except for the spring bloom because remineralization parallels primary production. Here, the pCO2pCO2 appears to be controlled by temperature.
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  • 20
    Publication Date: 2017-08-08
    Description: The Masaya Caldera Complex has been the site of three highly explosive basaltic eruptions within the last six thousand years. A Plinian eruption ca. 2 ka ago formed the widespread deposits of the Masaya Triple Layer. We distinguish two facies within the Masaya Triple Layer from each other: La Concepción facies to the south and Managua facies to the northwest. These two facies were previously treated as two separated deposits (La Concepción Tephra and the Masaya Triple Layer of Pérez and Freundt, 2006) because of their distinct regional distribution and internal architectures. However, chemical compositions of bulk rock, matrix and inclusion glasses and mineral phases demonstrate that they are the product of a single basaltic magma batch. Additionally, a marker bed containing fluidal-shaped vesicular lapilli allowed us to make a plausible correlation between the two facies, also supported by consistent lateral changes in lithologic structure and composition, thickness and grain size. We distinguish 10 main subunits of the Masaya Triple Layer (I to X), with bulk volumes ranging between 0.02 and 0.22 km3, adding up to 0.86 km3 (0.4 km3 DRE) for the entire deposit. Distal deposits identified in two cores drilled offshore Nicaragua, at a distance of ∼ 170 km from the Masaya Caldera Complex, increase the total tephra volume to 3.4 km3 or ∼ 1.8 km3 DRE of erupted basaltic magma. Isopleth data of five major fallout subunits indicate mass discharges of 106 to 108 kg/s and eruption columns of 21 to 32 km height, affected by wind speeds of 〈 2 m/s to ∼ 20 m/s which increased during the course of the multi-episodic eruption. Magmatic Plinian events alternated with phreatoplinian eruptions and phreatomagmatic explosions generating surges that typically preceded breaks in activity. While single eruptive episodes lasted for few hours, the entire eruption probable lasted weeks to months. This is indicated by changes in atmospheric conditions and ash-layer surfaces that had become modified during the breaks in activity. The Masaya Triple Layer has allowed to reconstruct in detail how a basaltic Plinian eruption develops in terms of duration, episodicity, and variable access of external water to the conduit, with implications for volcanic hazard assessment.
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  • 21
    Publication Date: 2019-09-23
    Description: The chemical and isotopic composition of pore fluids is presented for five deep-rooted mud volcanoes aligned on a transect across the Gulf of Cadiz continental margin at water depths between 350 and 3860 m. Generally decreasing interstitial Li concentrations and Sr-87/Sr-86 ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin. Although highest Li concentrations at the near-shore mud volcanoes coincide with high salinities derived from dissolution of halite and late-stage evaporites, clayey, terrigenous sediments are identified as the ultimate Li source to all pore fluids investigated. Light delta Li-7 values, partly close to those of hydrothermal vent fluids (delta Li-7: +11.9 parts per thousand), indicate that Li has been mobilized during high-temperature fluid/sediment or fluid/rock interactions in the deep sub-surface. Intense leaching of terrigenous clay has led to radiogenic Sr-87/Sr-86 ratios (similar to 0.7106) in pore fluids of the near-shore mud volcanoes. In contrast, non-radiogenic Sr-87/Sr-86 ratios (similar to 0.7075) at the distal locations are attributed to admixing of a basement-derived fluid component, carrying an isotopic signature from interaction with the basaltic crust. This inference is substantiated by temperature constraints from Li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures (>200 degrees C) for the least radiogenic pore fluids of the most distal location.Advective pore fluids in the off-shore reaches of the Gulf of Cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous, fine-grained sediments, resulting in a chemical and isotopic signature similar to that of fluids in near-shore ridge flank hydrothermal systems. This suggests that deep-rooted mud volcanoes in the Gulf of Cadiz represent a fluid pathway intermediate between mid-ocean ridge hydrothermal vent and shallow, marginal cold seep. Due to the thicker sediment coverage and slower fluid advection rates, the overall geochemical signature is shifted towards the sediment-diagenetic signal compared to ridge flank hydrothermal environments. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 22
    Publication Date: 2017-08-04
    Description: Continental shelves represent areas of highest economical and ecological importance. Nevertheless, these sedimentary systems remainpoorly understood due to a complex interplay of various factors and processeswhich results in highly individual construction schemes. Previous studies of sedimentary shelf systems have mainly focused on a limited number of cores, retrieved from Holocene fine-grained depocentres. As such, the relation between shelf architecture and sedimentary history remains largely obscure. Here,we present newdata fromthe NW Iberian shelf comprising shallow-seismic profiles, a large number of sediment cores, and an extended set of radiocarbon dates to reveal the Late Quaternary evolution of a low-accumulation shelf system in detail. OntheNWIberian shelf, threemain seismic units are identified. These overly a prominent erosional unconformity on top of the basement. The lowermost Unit 1 is composed of maximal 75-m thick, Late Tertiary to Pleistocene deposits. The youngest sediments of this unit are related to the last glacial sea-level fall. Unit 2 was controlled by the deglacial sea-level rise and shows a maximumthickness of 15 m. Finally, Unit 3 comprises deposits related to the late stage of sea-level rise and the modern sea-level highstand with a thickness of 4 m in mid-shelf position. Two pronounced seismic reflectors separate these main units from each other. Their origin is related to (1) exposure and ravinement processes during lower sea level, and (2) to reworking and re-deposition of coarse sediments during subsequent sea-level rise. According to the sediment core ground-truthing, sediments of the Late Tertiary to Pleistocene unit predominantly display homogenous fine sands with exceptional occurrences of palaeosols that indicate an ancient exposure surface. Fine sands which were deposited in the run of the last sea-level rise show a time-transgressive retrogradational development. The seismic reflectors, bounding the individual units, appear in the cores as 0.1 to 1-m thick deposits consisting either of shell gravels or siliceous coarse sands with gravels. The modern sea-level highstand stage is characterised by zonal deposition of mud forming a mud belt in mid-shelf position, and sediment starvation on outer shelf zones. Radiocarbon ages indicate that this mud beltwas the main depocentre for river-supplied fine material on the NWIberian shelf at least over the past 5.32 ka BP. The initial onset of this depocentre is proposed to be related to a shift in the balance between rate of sea-level rise and amount of terrigenous sediment supply. Various other stratigraphical shelf reconstructions reveal analogies in architecturewhich indicate that timing and shaping of the individual units on low-accumulation shelves is fundamentally controlled by eustatic sea-level changes. Other factors of local importance such as differential elevation of the basement and the presence of morphological barriers formed by rocky outcrops on the seafloor have additionally modifying influence on the sedimentary processes.
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  • 23
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    Elsevier
    In:  Journal of Volcanology and Geothermal Research, 186 (3/4). pp. 361-378.
    Publication Date: 2017-08-08
    Description: A model of diatreme evolution in a shallow marine setting is based on a multi-disciplinary analysis of diatremes in the Iblean Mountains (Sicily). The approach includes stratigraphic, volcanological, structural, petrologic and compositional data. We invoke a complex interplay of internal (rapid ascent and pyroclastic fragmentation of a volatile (CO2)-rich nephelinitic magma at depth) and external factors. These comprise hydroclastic explosions due to near-surface interaction of the rising particle/volatile mixture with seawater and water-saturated lime mud. Other external factors contributing to diatreme formation include regional and local tectonics (graben formation in pull-apart motion) combined with lateral pipe enlargement by bedrock-spalling and radial block subsidence into the diatreme pipe. We suggest that fragmentation of volatile-rich magma due to internal eruption forcing was fundamental in the formation of the Iblean shallow marine diatremes. Internal and external factors may act to a variable degree, however, during diatreme evolution in general.
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  • 24
    Publication Date: 2017-08-04
    Description: Newly acquired bathymetric and seismic reflection data have revealed mass-transport deposits (MTDs) on the northeastern Cretan margin in the active Hellenic subduction zone. These include a stack of two submarine landslides within the Malia Basin with a total volume of approximately 4.6 km(3) covering an area of about 135 km(2). These two MTDs have different geometry, internal deformations and transport structures. The older and stratigraphic lower MTD is interpreted as a debrite that fills a large part of the Malia Basin, while the second, younger MTD, with an age of at least 12.6 cal. ka B.P., indicate a thick, lens-shaped, partially translational landslide. This MTD comprises multiple slide masses with internal structure varying from highly deformed to nearly undeformed. The reconstructed source area of the older MTD is located in the westernmost Malia Basin. The source area of the younger MTD is identified in multiple headwalls at the slope-basin-transition in 450 m water depth. Numerous faults with an orientation almost parallel to the southwest-northeast-trending basin axis occur along the northern and southern boundaries of the Malia Basin and have caused a partial steepening of the slope-basin-transition. The possible triggers for slope failure and mass-wasting include (i) seismicity and (ii) movement of the uplifting island of Crete from neotectonics of the Hellenic subduction zone, and (iii) slip of clay-mineral-rich or ash-bearing layers during fluid involvement. (c) 2009 Elsevier B.V. All rights reserved.
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  • 25
    Publication Date: 2016-10-04
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  • 26
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    Elsevier
    In:  Earth and Planetary Science Letters, 288 (3-4). pp. 399-407.
    Publication Date: 2017-02-09
    Description: Newly pre-stack depth-migrated seismic images resolve the structural details of the western Java forearc and plate interface. The structural segmentation of the forearc into discrete mechanical domains correlates with distinct deformation styles. Approximately 2/3 of the trench sediment fill is detached and incorporated into frontal prism imbricates, while the floor sequence is underthrust beneath the décollement. Western Java, however, differs markedly from margins such as Nankai or Barbados, where a uniform, continuous décollement reflector has been imaged. In our study area, the plate interface reveals a spatially irregular, nonlinear pattern characterized by the morphological relief of subducted seamounts and thicker than average patches of underthrust sediment. The underthrust sediment is associated with a low velocity zone as determined from wide-angle data. Active underplating is not resolved, but likely contributes to the uplift of the large bivergent wedge that constitutes the forearc high. Our profile is located 100 km west of the 2006 Java tsunami earthquake. The heterogeneous décollement zone regulates the friction behavior of the shallow subduction environment where the earthquake occurred. The alternating pattern of enhanced frictional contact zones associated with oceanic basement relief and weak material patches of underthrust sediment influences seismic coupling and possibly contributed to the heterogeneous slip distribution. Our seismic images resolve a steeply dipping splay fault, which originates at the décollement and terminates at the sea floor and which potentially contributes to tsunami generation during co-seismic activity.
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  • 27
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    Elsevier
    In:  Ocean Modelling, 26 (1-2). pp. 47-59.
    Publication Date: 2018-10-23
    Description: The effects of spatial variations of the thickness diffusivity (K) appropriate to the parameterisation of [Gent, P.R. and McWilliams, J.C., 1990. Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr., 20, 150–155.] are assessed in a coarse resolution global ocean general circulation model. Simulations using three closures yielding different lateral and/or vertical variations in K are compared with a simulation using a constant value. Although the effects of changing K are in general small and all simulations remain biased compared to observations, we find systematic local sensitivities of the simulated circulation on K. In particular, increasing K near the surface in the tropical ocean lifts the depth of the equatorial thermocline, the strength of the Antarctic Circumpolar Current decreases while the subpolar and subtropical gyre transports in the North Atlantic increase by increasing K locally. We also find that the lateral and vertical structure of K given by a recently proposed closure reduces the negative temperature biases in the western North Atlantic by adjusting the pathways of the Gulf Stream and the North Atlantic Current to a more realistic position.
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  • 28
    Publication Date: 2019-07-03
    Description: Isis mud volcano is located on the upper slope of the Nile deep-sea fan and has been described as the surface expression of a deep-seated gas chimney [Loncke, L., Gaullier, V., Mascle, J., Vendeville, B., 2002. Shallow structure of the Nile deep-sea fan: interactions between structural heritage and salt tectonics; consequences on sedimentary dispersal. In: CIESM (Ed.), Turbidite systems and deep-sea fans of the Mediterranean and the Black seas. CIESM Workshop Series. vol. 17. Monaco]. Detailed geothermal and geochemical investigations of Isis MV have been carried out during the NAUTINIL (2003) and MIMES (2004) cruises within the framework of the Euro-margins/Mediflux project. Sediment temperatures of more than 40 °C at 10 m below the seafloor at the center of the mud volcano indicate an exceptionally high level of activity. Rapidly decreasing temperature gradients away from the center support the hypothesis of a dominantly axisymmetric functioning of Isis MV. The microbathymetry along dive tracks of the submersible Nautile reveals the presence of terraces and shows that the temperature gradients at shallow sediment depth follow the morphology. At the center, porewater profiles are characterized by a rapid decrease of chlorinity within the uppermost meter of the sediments, whereas the chlorinity of cores taken at short distances away is equal to bottom water values. Applying simple analytical models to the data provides evidence of recent mud volcano activity but no straightforward explanation of the observed anomalies, which points to a transient regime of variable fluid flow, possibly accompanied by episodic mud eruptions. Numerical modeling suggests that rapid cooling of the sediment column and downward progression of the sharp decrease in porewater chlorinity observed between the two cruises is related to episodic infiltration of bottom seawater into the mud.
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  • 29
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 . pp. 1924-1944.
    Publication Date: 2019-08-14
    Description: In this study the sulfur cycle in the organic-rich mud belt underlying the highly productive upwelling waters of the Namibian shelf is quantified using a 1D reaction-transport model. The model calculates vertical concentration and reaction rate profiles in the top 500 cm of sediment which are compared to a comprehensive dataset which includes carbon, sulfur, nitrogen and iron compounds as well as sulfate reduction (SR) rates and stable sulfur isotopes (32S, 34S). The sulfur dynamics in the well-mixed surface sediments are strongly influenced by the activity of the large sulfur bacteria Thiomargarita namibiensis which oxidize sulfide (H2S) to sulfate () using sea water nitrate () as the terminal electron acceptor. Microbial sulfide oxidation (SOx) is highly efficient, and the model predicts intense cycling between and H2S driven by coupled SR and SOx at rates exceeding 6.0 mol S m−2 y−1. More than 96% of the SR is supported by SOx, and only 2–3% of the pool diffuses directly into the sediment from the sea water. A fraction of the produced by Thiomargarita is drawn down deeper into the sediment where it is used to oxidize methane anaerobically, thus preventing high methane concentrations close to the sediment surface. Only a small fraction of total H2S production is trapped as sedimentary sulfide, mainly pyrite (FeS2) and organic sulfur (Sorg) (∼0.3 wt.%), with a sulfur burial efficiency which is amongst the lowest values reported for marine sediments (〈1%). Yet, despite intense SR, FeS2 and Sorg show an isotope composition of ∼5 ‰ at 500 cm depth. These heavy values were simulated by assuming that a fraction of the solid phase sulfur exchanges isotopes with the dissolved sulfide pool. An enrichment in H2S of 34S towards the sediment-water interface suggests that Thiomargarita preferentially remove H232S from the pore water. A fractionation of 20–30‰ was estimated for SOx (εSOx) with the model, along with a maximum fractionation for SR (εSR–max) of 100‰. These values are far higher than previous laboratory-based estimates for these processes. Mass balance calculations indicate negligible disproportionation of autochthonous elemental sulfur; an explanation routinely cited in the literature to account for the large fractionations in SR. Instead, the model indicates that repeated multi-stepped sulfide oxidation and intracellular disproportionation by Thiomargarita could, in principle, allow the measured isotope data to be simulated using much lower fractionations for εSOx (5‰) and εSR (78‰).
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  • 30
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    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 56 (13-14). pp. 835-842.
    Publication Date: 2019-09-23
    Description: During the second cruise of the AnSlope project, the hydrography and velocity fields within a descending gravity plume in the northwestern Ross Sea Shelf area were sampled at high resolution. The observations give insights into small-scale fluctuations of the three-dimensional velocity field in and around the core of a strong gravity current, associated with peak velocities close to 2 m/s. There are two distinct layers of high acoustic backscatter (at 300 kHz) near the seabed associated with increased velocity variance and Richardson numbers near 0.25, suggesting that the high backscatter is caused by increased levels of turbulence resulting in increased acoustic Bragg scattering. (C) 2008 Elsevier Ltd. All rights reserved.
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  • 31
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 . pp. 1656-1674.
    Publication Date: 2016-11-01
    Description: The variability of two modes of Labrador Sea Water (LSW) (upper and deep Labrador Sea Water) and their respective spreading in the interior North Atlantic Ocean are investigated by means of repeated ship surveys carried out along the zonal WOCE line A2/AR19 located at 43–48°N (1993–2007) and along the GOOS line at about 48–51°N (1997–2002). Hydrographic section data are complemented by temperature, salinity, and velocity time series recorded by two moorings. They have been deployed at the western flank of the Mid-Atlantic Ridge (MAR) in the Newfoundland Basin during 1996–2004. The analysis of hydrographic anomalies at various longitudes points to a gradual eastward propagation of LSW-related signals, which happens on time scales of 3–6 years from the formation region towards the MAR. Interactions of the North Atlantic Current (NAC) with the Deep Western Boundary Current (DWBC) close to Flemish Cap point to the NAC being the main distributor of the different types of LSW into the interior of the Newfoundland Basin. Comparisons between the ship data and the mooring records revealed that the mooring sites are located in a region affected by highly variable flow. The mooring time series demonstrate an elevated level of variability with eddy activity and variability associated with the NAC considerably influencing the LSW signals in this region. Hydrographic data taken from Argo profiles from the vicinity of the mooring sites turned out to mimic quite well the temporal evolution captured by the moorings. There is some indication of occasional southward flow in the LSW layer near the MAR. If this can be considered as a hint to an interior LSW-route, it is at least of minor importance in comparison to the DWBC. It acts as an important supplier for the interior North Atlantic, distributing older and recently formed LSW modes southward along the MAR.
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  • 32
    Publication Date: 2019-09-23
    Description: Breakup of the North Atlantic during the early tertiary was accompanied by widespread and massive magmatism, resulting in the coverage of large areas of the North Atlantic with flood basalts. These flood basalts hamper seismic investigations of underlying sequences and thus the understanding of the rifting, subsidence and evolution of the margin which, in turn, increases the risk for hydrocarbon exploration. In this paper we present a methodology for the simultaneous joint inversion of diverse geophysical datasets, i.e. free air gravity and magnetotelluric soundings (MT) using seismic a priori constraints. The attraction of the joint inversion approach is that different geophysical measurements are sensitive to different properties of the sub-surface, so through joint inversion we significantly reduce the null space and produce a single model that fits all datasets within a predefined tolerance. Using sensitivity analysis of synthetic data, we show how each data set contains complementary important information of the supra and sub-basalt structure. While separate inversions of individual datasets fail to image through the basalt layer, our joint inversion approach leads to a much improved sub-basalt structure. Application of the joint inversion algorithm to satellite gravity data and MT data acquired on the FLARE10 seismic line south west of Faroe islands supports the existence of a 1 km to 2 km thick low velocity region that might be indicative of the existence of a sedimentary basin underneath the basalt layer. Though in this paper we demonstrate the use of joint inversion on a sub-basalt target, we believe it has wider applicability to other areas where conventional seismic imaging fails.
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  • 33
    Publication Date: 2017-07-21
    Description: The sediment temperature distribution at mud volcanoes provides insights into their activity and into the occurrence of gas hydrates. If ambient pressure and temperature conditions are close to the limits of the gas hydrate stability field, the sediment temperature distribution not only limits the occurrence of gas hydrates, but is itself influenced by heat production and consumption related to the formation and dissociation of gas hydrates. Located in the Sorokin Trough in the northern Black Sea, the Dvurechenskii mud volcano (DMV) was in the focus of detailed investigations during the M72/2 and M73/3a cruises of the German R/V Meteor and the ROV Quest 4000 m in February and March 2007. A large number of in-situ sediment temperature measurements were conducted from the ROV and with a sensor-equipped gravity corer. Gas hydrates were sampled in pressurized cores using a dynamic autoclave piston corer (DAPC). The thermal structure of the DMV suggests a regime of fluid flow at rates decreasing from the summit towards the edges of the mud volcano, accompanied by intermittent mud expulsion at the summit. Modeled gas hydrate dissociation temperatures reveal that the gas hydrates at the DMV are very close to the stability limits. Changes in heat flow due to variable seepage rates probably do not result in changes in sediment temperature but are compensated by gas hydrate dissociation and formation. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 34
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    Elsevier
    In:  Comparative Biochemistry and Physiology A - Molecular and Integrative Physiology, 153 . pp. 278-283.
    Publication Date: 2017-12-11
    Description: It is still a matter of debate whether cephalopods can detect sound frequencies above 400 Hz. So far there is no proof for the detection of underwater sound above 400 Hz via a physiological approach. The controversy of whether cephalopods have a sound detection ability above 400 Hz was tested using the auditory brainstem response (ABR) approach, which has been successfully applied in fish, crustaceans, amphibians, reptiles and birds. Using ABR we found that auditory evoked potentials can be obtained in the frequency range 400 to 1500 Hz (Sepiotheutis lessoniana) and 400 to 1000 Hz (Octopus vulgaris), respectively. The thresholds of S. lessoniana were generally lower than those of O. vulgaris.
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  • 35
    Publication Date: 2019-09-23
    Description: The skill of numerical Lagrangian drifter trajectories in three numerical models is assessed by comparing these numerically obtained paths to the trajectories of drifting buoys in the real ocean. The skill assessment is performed using the two-sample Kolmogorov-Smirnov statistical test. To demonstrate the assessment procedure, it is applied to three different models of the Agulhas region. The test can either be performed using crossing positions of one-dimensional sections in order to test model performance in specific locations, or using the total two-dimensional data set of trajectories. The test yields four quantities: a binary decision of model skill, a confidence level which can be used as a measure of goodness-of-fit of the model, a test statistic which can be used to determine the sensitivity of the confidence level, and cumulative distribution functions that aid in the qualitative analysis. The ordering of models by their confidence levels is the same as the ordering based on the qualitative analysis, which suggests that the method is suited for model validation. Only one of the three models, a 1/10 degree two-way nested regional ocean model, might have skill in the Agulhas region. The other two models, a 1/2 degree global model and a 1/8 degree assimilative model, might have skill only on some sections in the region.
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  • 36
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    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 56 . pp. 2216-2234.
    Publication Date: 2016-11-01
    Description: Cold-water coral ecosystems building cold-water carbonate mounds occur worldwide and are especially developed along the European margin, from northern Norway to the Gulf of Cadiz. A remarkable mound province is documented southwest of Ireland along the Porcupine and Rockall Banks. In this area carbonate mounds are formed in water depths between 500 and 1200 m and are often densely settled by cold-water coral ecosystems offering many ecological niches for benthic foraminifera. We investigated total (unstained) benthic foraminiferal assemblages from surface sediments (0–1 cm, 〉63 μm size fraction) of this region with the aim to trace their distribution patterns and to test if they can be used as bioindicators for facies characterization in different parts of carbonate mound systems. Our quantitative data were further statistically treated with non-metric multidimensional scaling (nMDS) based on Bray–Curtis similarity matrix to highlight community patterns that were not readily apparent. Our results indicate that different benthic foraminiferal assemblages characterize different facies along cold-water carbonate mounds and are related to the environmental conditions and available substrates. The following facies can be described: (1) the Off-Mound Facies is dominated by uvigerinids and other infaunal species; (2) the Dropstone Facies is characterized by infaunal Globocassidulina subglobosa and attached-epifaunal Cibicidoides sp.; (3) the Dead Coral Facies is characterised by epifaunal species (e.g., Planulina ariminensis, Hanzawaia boueana) and infaunal species (Spiroplectinella wrightii, Angulogerina angulosa, Epistominella vitrea); (4) the Living Coral Facies includes both infaunal and epifaunal species, but is dominated by the epifaunal Discanomalina coronata; and (5) the Sandwave Facies contains high abundances of epifaunal species including D. coronata. Based on this distribution, we propose D. coronata, as an indicator species to identify active mounds and/or living cold-water coral ecosystems. Our results also emphasise the importance of studying the small size fractions that yield many infaunal species. A causal link exists between distribution patterns of benthic foraminifera and cold-water coral facies, thus providing an independent tool to identify and describe the different facies in this setting.
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  • 37
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    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 56 (13-14). pp. 796-817.
    Publication Date: 2019-09-23
    Description: Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the Ross Sea when High Salinity Shelf Water exits the shelf through Drygalski Trough. Joides Trough, immediately to the east, offers an additional escape route for less saline Shelf Water, while the Glomar Challenger Trough still farther east is a major pathway for export of the once supercooled low-salinity Ice Shelf Water that forms under the Ross Ice Shelf. The Drygalski Trough gravity currents increase in thickness from ∼100 to ∼400 m on proceeding downslope from ∼600 m (the shelf break) to 1200 m (upper slope) sea floor depth, while turning sharply to the west in response to the Coriolis force during their descent. The mean current pathway trends ∼35° downslope from isobaths. Benthic-layer current and thickness are correlated with the bottom water salinity, which exerts the primary control over the benthic-layer density. A 1-year time series of bottom-water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of Shelf Water export through Drygalski Trough. These cold (〈−1 °C), salty (〉34.75) pulses correlate with strong downslope bottom flow. Extreme examples occurred during austral summer/fall 2003, comprising concentrated High Salinity Shelf Water (−1.9 °C; 34.79) and approaching 1.5 m s−1 at descent angles as large as ∼60° relative to the isobaths. Such events were most common during November–May, consistent with a northward shift in position of the dense Shelf Water during austral summer. The coldest, saltiest bottom water was measured from mid-April to mid-May 2003. The summer/fall export of High Salinity Shelf Water observed in 2004 was less than that seen in 2003. This difference, if real, may reflect the influence of the large iceberg C-19 over Drygalski Trough until its departure in mid-May 2003, when there was a marked decrease in the coldest, saltiest gravity current adjacent to Drygalski Trough. Northward transport of cold, saline, recently ventilated Antarctic Bottom Water observed in March 2004 off Cape Adare was ∼1.7 Sv, including ∼0.4 Sv of High Salinity Shelf Water.
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  • 38
    Publication Date: 2018-01-05
    Description: Salt tectonics and mud volcanism in the Latakia and Cyprus Basin, eastern Mediterranean, is investigated by means of swath sounding, reflection seismics and side-scan data as well as by camera and video sledge observations. Both basins are located east of Cyprus and are associated with the collision front between the African and Anatolian plate. The Pliocene–Quaternary sediment succession is underlain by up to 1 km thick Messinian evaporites. Both thick-skinned plate tectonic and thin-skinned salt tectonic control fluid dynamics and associated mud volcanism in the Latakia and Cyprus Basin as well as at the Troodos Latacia Culmination, which separates both basins. An end-member model is proposed which explains the presence of elongated topographic highs and trenches along the Troodos Larnaca Culmination and south of it by gravity gliding of the Messinian evaporites and associated fluid migration. Thin-skinned extension in the Troodos Larnaca Culmination and boudinage, respectively, facilitate fluid flow through and out of the evaporites. The fluid or mud flow dissolutes the salt layer and creates elongated trenches. Mud intrudes into the Pliocene–Quaternary sediments above the trenches. Consequently, the overburden is thickened and forms morphological ridges. South of the culmination the evaporites and overburden are folded due to thin-skinned shortening of the evaporites. In one instance fluid extrusion out of the evaporites is inferred from seismic data interpretation. The outflow caused a volume reduction and collapse of the evaporites. Mud volcanoes and fold anticlines align above deep-rooted transpressional fault systems which are associated with the African–Anatolian collision zone. The faults may act as conduits for rising fluids. In the western part of the survey area, where the Cyprus Arc strikes almost West–East and the collision occurred more frontal and stress was highest, mud volcanoes emerged. Further to the east, where the Cyprus Arc runs SW–NE and sinistral strike-slip has been proposed, fold anticlines evolved. Particular mud volcanoes and folds emerged prior to the deposition of the Messinian evaporites. The undisturbed upper Pleistocene sequences as well as the absence of significant mud outflow on the seafloor strongly suggest that the main fluid dynamic ceased.
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  • 39
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    Elsevier
    In:  Continental Shelf Research, 29 (1). pp. 61-77.
    Publication Date: 2019-09-23
    Description: We present detailed observations of internally generated turbulence in a sheared, stratified natural flow, as well as an analysis of the external factors leading to its generation and temporal variability. Multi-month time series of vertical profiles of velocity, acoustic backscatter (0.5 Hz), and turbulence parameters were collected with two moored acoustic Doppler current profilers (ADCPs) in the Hudson River estuary, and estuary-long transects of water density were collected 30 times. ADCP backscatter is used for visualization of coherent turbulent structures and evaluation of surface wave biases to the turbulence measurements. Benefits of the continuous long-term turbulence record include our capturing: (1) the seasonality of turbulence due to changing riverflow, (2) hysteresis in stratification and turbulence over the fortnightly cycle of tidal range, and (3) intermittent events such as breaking internal waves. Internal mixing layers (IMLs) are defined as turbulent regions above the logarithmic velocity layer, and the bottom boundary layer (BBL) is defined as the continuously turbulent range of heights above the bed. A cross-correlation analysis reveals how IML and BBL turbulence vary with stratification and external forcing from tidal range, river flow, and winds. Turbulence in both layers is maximal at spring tide and minimal when most stratified, with one exception IML turbulence at a site with changing channel depth and width is maximal at times of maximum stratification and freshwater input.
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  • 40
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    Elsevier
    In:  Geochimica et Cosmochimica Acta, 73 . pp. 2645-2659.
    Publication Date: 2017-09-27
    Description: Nd concentration and isotope data have been obtained for the Canada, Amundsen, and Makarov Basins of the Arctic Ocean. A pattern of high Nd concentrations (up to 58 pM) at shallow depths is seen throughout the Arctic, and is distinct from that generally seen in other oceans where surface waters are relatively depleted. A range of isotopic variations across the Arctic and within individual depth profiles reflects the different sources of waters. The dominant source of water, and so Nd, is the Atlantic Ocean, with lesser contributions from the Pacific and Arctic Rivers. Radiogenic isotope Nd signatures (up to epsilon(Nd) = -6.5) can be traced in Pacific water flowing into the Canada Basin. Waters from rivers draining older terrains provide very unradiogenic Nd (down to epsilon(Nd) = -14.2) that can be traced in surface waters across much of the Eurasian Basin. A distinct feature of the Arctic is the general influence of the shelves on the Nd concentrations of waters flowing into the basins, either from the Pacific across the Chukchi Sea, or from across the extensive Siberian shelves. Water-shelf interaction results in an increase in Nd concentration without significant changes in salinity in essentially all waters in the Arctic, through processes that are not yet well understood. In estuarine regions other processes modify the Nd signal of freshwater components supplied into the Arctic Basin, and possibly also contribute to sedimentary Nd that may be subsequently involved in sediment-water interactions. Mixing relationships indicate that in estuaries, Nd is removed from major river waters to different degrees. Deep waters in the Arctic are higher in Nd than the inflowing Atlantic waters, apparently through enrichments of waters on the shelves that are involved in ventilating the deep basins. These enrichments generally have not resulted in major shifts in the isotopic compositions of the deep waters in the Makarov Basin (epsilon(Nd) similar to -10.5), but have created distinctive Nd isotope signatures that were found near the margin of the Canada Basin (with epsilon(Nd) similar to -9.0). The deep waters of the Amundsen Basin are also distinct from the Atlantic waters (with epsilon(Nd) = -12.3), indicating that there has been limited inflow from the adjacent Makarov Basin through the Lomonosov Ridge. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 41
    Publication Date: 2017-02-09
    Description: Pressure solution is one of the main deformation mechanisms for lithify and stress release in the rocks from shallow subduction zones. We observed temperature-dependent pressure solution development in naturally deformed shale in Shimanto accretionary complex in southwest Japan. The pressure solution develops with shear-dominated or co-axial-dominated deformation. We evaluated apparent activation energy by applying the constitutive equation of pressure solution creep to the temperature-dependent relations. The activation energy of each deformation type was estimated as 18 kJ mol− 1 for shear-dominated and 45 kJ mol− 1 for co-axial-dominated shale. The energies enable us to speculate rate-limiting processes of pressure solution i.e. dissolution, diffusion and precipitation, by comparing the energies obtained in this study with energies had been measured by experiments. The lower activation energy estimated here was similar with that of diffusion. The similarity indicates that possible rate-limiting process of shale deformation in shallow subduction zone would be diffusion. The difference of energy between deformation types can be explained by distinctive grain boundary structure.
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  • 42
    Publication Date: 2012-10-22
    Description: The Mg- and Si-rich nature of the sub-cratonic lithospheric mantle (SCLM) beneath the Kaapvaal Craton indicates extensive melt depletion, followed by a Si-enrichment process. Six highly silica enriched peridotites from Kimberley containing high amounts of orthopyroxene (Opx) or garnet (Grt) that are locally concentrated in clots, were investigated to constrain the timing and nature of the Si-enrichment process. A clinopyroxene-bearing lherzolite containing an Opx-clot was studied to quantify the effects of recent metasomatism on the Si-enriched samples. Minerals from the lherzolite, together with Opx from harzburgites and Opx- and Grt-clots have Hf–Nd isotope ratios at the time of kimberlite eruption, 90 Ma, comparable to group I kimberlites and are close to trace element equilibrium with kimberlitic melts. This implies the xenoliths underwent major interaction with kimberlitic melts close to the time of kimberlite eruption. Harzburgites and mineral clots record equilibration pressures and temperatures of, respectively, between 3.5–4.3 GPa and 930–1060 °C. The garnets in Opx-clots have low Lu/Hf and εHf(t) −15, whereas garnets from Grt-clots have high Lu/Hf and εHf(t) +10. In contrast, Grt from both Grt- and Opx-clots have low Sm/Nd and εNd −10. The whole rock platinum group element (PGE) concentrations are an order of magnitude higher in the Grt-clot than the Opx-clot. Measured 187Os/188Os range from 0.1085 to 0.1222. The Grt-clot bearing sample yields Nd–Hf–Os isotope model ages that suggest formation in the Neoproterozoic (∼650 Ma). In contrast, an Opx-clot yields TRD ages of 2.8 Ga, which is interpreted as the time of formation of the host harzburgite. The Opx-clots and host harzburgites have comparable Lu–Hf isotope systematics that imply Opx growth at ∼1.3 Ga and hence their formation is not related to the Grt-clots. Garnets from Opx- and Grt-clots have elevated high-field strength element (HFSE) concentrations, and lack HFSE depletion relative to other trace elements with comparable degrees of incompatibility in the mantle (La/Nb 〈 0.5). In addition, calculated melts in equilibrium with Grt have strongly fractionated REE (Nd/Yb 〉 300) and HREE depletion (YbN 〈 0.1) suggesting equilibration with a hydrous melt that is more HREE depleted than a kimberlitic melt. Previous models that related Si-enrichment to subduction are inconsistent with the lack of HFSE depletion (La/Nb 〈 0.5). Therefore the favoured model for Opx- and Grt-clot formation is infiltration of a hydrous melt in a within plate geodynamical environment associated with volcanism in the Mid-proterozoic and Neoproterozoic, respectively. This implies that Si-enrichment of the Kaapvaal SCLM may be a consequence of numerous localised magmatic events rather than a single craton-wide process.
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  • 43
    Publication Date: 2014-01-27
    Description: A detailed investigation into the performance of two flow injection-chemiluminescence (FI-CL) manifolds (with and without a preconcentration column) for the determination of sub-nanomolar dissolved iron (Fe(II) + Fe(III)), following the reduction of Fe(III) by sulphite, in seawater is described. Kinetic experiments were conducted to examine the efficiency of reduction of inorganic Fe(III) with sulphite under different conditions and a rigorous study of the potential interference caused by other transition metals present in seawater was conducted. Using 100 μM concentrations of sulphite a reduction time of 4 h was sufficient to quantitatively reduce Fe(III) in seawater. Under optimal conditions, cobalt(II) and vanadium(IV)/(III) were the major positive interferences and strategies for their removal are reported. Specifically, cobalt(II) was masked by the addition of dimethylglyoxime to the luminol solution and vanadium(IV) was removed by passing the sample through an 8-hydroxyquinoline column in a low pH carrier stream. Manganese(II) also interfered by suppression of the CL response but this was not significant at typical open ocean concentrations. © 2009 Elsevier B.V. All rights reserved.
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  • 44
    Publication Date: 2014-01-27
    Description: This paper presents the results of an inter-comparison exercise undertaken to test the reliability and performance of a voltammetric in situ profiling system (VIP system) and carried out by partners based in Italy, Sweden, Switzerland and the UK. The VIP system was designed to allow in situ simultaneous monitoring of the dynamic fractions (i.e. the maximum potentially bioavailable fractions) of Cu(II), Pb(II) and Cd(II) in natural waters at a frequency of 2-3 analyses h - 1. The four participating groups used the VIP systems under laboratory conditions to determine dissolved concentrations of Cu, Pb and Cd in river, estuarine and coastal water reference materials (SLRS-3/4, SLEW-2/3 and CASS3/4, respectively). The accuracy of the VIP method was comparable to that of established methodologies, including inductively coupled plasma mass spectrometry and voltammetric methods using mercury-electrodes. The VIP systems were also applied to determine the dynamic fractions of the target analytes in freshly collected samples ex situ, as well as in situ in contrasting European marine waters. There was good agreement between the concentrations of the dynamic metal fractions determined in laboratory analyses, and observed during the simultaneous deployment of up to five VIP instruments for periods of several hours in coastal waters. The simultaneous in situ deployment of two VIP instruments in an estuary showed a consistent analytical performance over several days of continuous operation. The results of this inter-comparison exercise show that the VIP system is a reliable submersible probe for accurate, sensitive and high resolution in situ monitoring of dissolved metal fractions in the picomolar (Cd, Pb) and nanomolar (Cu) concentration ranges. © 2009 Elsevier B.V. All rights reserved.
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  • 45
    Publication Date: 2016-06-15
    Description: Continental rifting at the Vøring Margin off mid-Norway was initiated during the earliest Eocene (~54 Ma), and large volumes of magmatic rocks were emplaced during and after continental breakup. In 2003, a marine survey collecting ocean bottom seismometer, single-channel re!ection, and magnetic data was conducted on the Norwegian Margin to constrain continental breakup and early sea!oor spreading processes. The pro"le described here crosses the northern part of the Vøring Plateau, and the crustal velocity model was constructed through a combination of ray-tracing and forward gravity modeling, the latter corrected for the thermal effects remaining from the sea!oor spreading. We found a maximum igneous crustal thickness of 18 km, decreasing to 6.5 km over the "rst ~6 M.y. after continental breakup. Both the volume and the duration of excess magmatism are about twice as large as that of the Møre Margin south of the East Jan Mayen Fracture Zone, which offsets the two margin segments by ~170 km. A similar reduction in magmatism occurs to the north over an along-margin distance of ~150 km to the Lofoten Margin, but without a margin offset. Both the geochemical data and the mean P-wave velocity indicate that there is active mantle upwelling combined with a moderate temperature increase during the earliest mantle melting at the Vøring Margin. The mean P-wave velocity versus crustal thickness also indicates that there is a transition from convection dominated to temperature dominated magma production ~2 M.y. after breakup. The magnetic data were used to derive plate half-spreading rates for the Northern Vøring Margin, which are very similar to that obtained at the Møre Margin. There is a strong correlation between magma productivity and early plate spreading rate, suggesting a common cause. A model for the breakup-related magmatism should be able to explain this correlation, but also the magma production peak at breakup, the along-margin magmatic segmentation, and the active mantle upwelling. Proposed end-member hypotheses comprise elevated uppermantle temperatures caused by a hot mantle plume, or edge-driven small-scale convection !uxing mantle rocks through the melt zone. Edge-driven convection does not easily explain these observations, but a mantle plume model in which buoyant plume material !ows laterally to pond in the rift-topography at the base of the lithosphere close to breakup time is promising: When the continents break apart, the hot and buoyant plume-material can !ow up into the rift zone from surrounding areas as the rift transits to drift, and the excess temperature of this material will then cause excess magmatism which dies off as the rift-restricted material is spent. The buoyancy of the plume-material may in addition cause active upwelling which can increase the melting furthermore, and also increase the force on the plate boundaries to enhance plate spreading rate. This conceptual model explains how both excess magmatism and spreading rate will be reduced similarly with time as the plume material is consumed by plate spreading, and thus correlate.
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  • 46
    Publication Date: 2019-09-23
    Description: Our analysis of geoacoustic data from the Middle American margin provides an insight into the formation and evolution mechanisms of mound structures observed on the continental slope offshore Costa Rica. Based on high-resolution deep-towed sidescan sonar and sub-bottom profiler (SBP) data six different mound and fluid seepage structures at the Hongo mound field are characterized in detail. The Hongo mound field is located on the lower continental slope offshore Nicoya peninsula in the prolongation of the subducting Nicoya fracture zone. The mounds have oval to circular shapes with diameters of 500-1600 m and relief heights of 60-100 m. High backscatter anomalies near the mound summits indicate carbonate precipitation and focused fluid seepage activity within the last 10 ka. The data do not show evidence for mud extrusions and the structures were probably formed by a combination of carbonate precipitation and mud diapirism. Based on seismic stratigraphy analysis, mud diapirism is at least active since 42.5-57 ka and average vertical growth rates vary between 6-24 cm/ka. However, if diapirism represents the dominant mound evolution mechanism, mound heights of 80 m point to much older mound ages of 330-1330 ka. (C) 2009 Elsevier B.V. All rights reserved.
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  • 47
    Publication Date: 2016-11-01
    Description: A combination of 2-year-long mooring-based measurements and snapshot conductivity–temperature–depth (CTD) observations at the continental slope off Spitsbergen (81°30′N, 31°00′E) is used to demonstrate a significant hydrographic seasonal signal in Atlantic Water (AW) that propagates along the Eurasian continental slope in the Arctic Ocean. At the mooring position this seasonal signal dominates, contributing up to 50% of the total variance. Annual temperature maximum in the upper ocean (above 215 m) is reached in mid-November, when the ocean in the area is normally covered by ice. Distinct division into ‘summer’ (warmer and saltier) and ‘winter’ (colder and fresher) AW types is revealed there. Estimated temperature difference between the ‘summer’ and ‘winter’ waters is 1.2 °C, which implies that the range of seasonal heat content variations is of the same order of magnitude as the mean local AW heat content, suggesting an important role of seasonal changes in the intensity of the upward heat flux from AW. Although the current meter observations are only 1-year long, they hint at a persistent, highly barotropic current with little or no seasonal signal attached.
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  • 48
    Publication Date: 2017-08-04
    Description: We report on a multidisciplinary study of cold seeps explored in the Central Nile deep-sea fan of the Egyptian margin. Our approach combines in situ seafloor observation, geophysics, sedimentological data, measurement of bottom-water methane anomalies, pore-water and sediment geochemistry, and 230Th/U dating of authigenic carbonates. Two areas were investigated, which correspond to different sedimentary provinces. The lower slope, at ∼ 2100 m water depth, indicates deformation of sediments by gravitational processes, exhibiting slope-parallel elongated ridges and seafloor depressions. In contrast, the middle slope, at ∼ 1650 m water depth, exhibits a series of debris-flow deposits not remobilized by post-depositional gravity processes. Significant differences exist between fluid-escape structures from the two studied areas. At the lower slope, methane anomalies were detected in bottom-waters above the depressions, whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities. Carbonate U/Th age dates (∼ 8 kyr BP), pore-water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past. In contrast, large (∼ 1 km2) carbonate-paved areas were discovered in the middle slope, with U/Th isotope evidence for ongoing carbonate precipitation during the Late Holocene (since ∼ 5 kyr BP at least). Our results suggest that fluid venting is closely related to sediment deformation in the Central Nile margin. It is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of ‘fossil’ carbonate ridges, whereas pervasive diffuse flow prevails at the unfailed middle slope.
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  • 49
    facet.materialart.
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    Elsevier
    In:  [Talk] In: Goldschmidt Conference 2009 "Challenges to Our Volatile Planet", 21.-26.06.2009, Davos, Switzerland ; A1249 .
    Publication Date: 2019-09-23
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  • 50
    facet.materialart.
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    Elsevier
    In:  Earth and Planetary Science Letters, 280 (1/4). pp. 159-166.
    Publication Date: 2016-10-14
    Description: Various theoretical and numerical models have been proposed in order to explain joint formation and spacing in layered rock series. However, most of these models assume that the interfaces between the rock layers are perfectly welded, i.e. no slip occurs, and that all the layers are subjected to the same remote strain due to various processes (e.g. tectonic processes). Other factors may also induce extensional strain in rocks, e.g. phase transformations. However, such processes may induce different amounts of strain on the layers in a rock series leading to a strain mismatch between these layers. In this paper, we present a 1-D finite difference linear elastic model which allows joint formation within the middle layer in a three-layer rock series and is induced by a strain mismatch between the fractured, central layer and the surrounding matrix. Furthermore, the central layer in our model is not necessarily welded to the matrix layers and is allowed to slip along the interfaces between these layers if the shear strength of the material at the interface is reached. We find that the final fracture spacing to layer thickness ratio (S/Tf) in such layered systems is directly proportional to the ratio of the tensile and shear strength of the material. Changes in the material properties such as the shear modulus or Young's modulus do not affect these results. A natural analog of joint formation driven by phase transformations is found in the orthopyroxenite dykes of the Leka Ophiolite Complex (LOC), Norway. Joint formation in orthopyroxenite dykes results from serpentinization-driven expansion of the surrounding dunite matrix. Detailed field studies and measurements (583 sample points) yield S/Tf ratios between 0.1 and 1.0 with a mean value of 0.45 ± 0.20. We demonstrate that the strain mismatch-driven joint formation associated with interfacial slip explains the low S/Tf ratios obtained from field measurements and may also help us constrain rock strength.
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  • 51
    Publication Date: 2019-12-31
    Description: Inflow of Atlantic water (AW) from Fram Strait and the Barents Sea into the Arctic Ocean conditions the intermediate (100–1000 m) waters of the Arctic Ocean Eurasian margins. While over the Siberian margin the Fram Strait AW branch (FSBW) has exhibited continuous dramatic warming beginning in 2004, the tendency of the Barents Sea AW branch (BSBW) has remained poorly known. Here we document the contrary cooling tendency of the BSBW through the analysis of observational data collected from the icebreaker Kapitan Dranitsyn over the continental slope of the Eurasian Basin in 2005 and 2006. The CTD data from the R.V. Polarstern cruise in 1995 were used as a reference point for evaluating external atmospheric and sea-ice forcing and oxygen isotope analysis. Our data show that in 2006 the BSBW core was saltier (by ∼0.037), cooler (by ∼0.41 °C), denser (by ∼0.04 kg/m3), deeper (by 150–200 m), and relatively better ventilated (by 7–8 μmol/kg of dissolved oxygen, or by 1.1–1.7% of saturation) compared with 2005. We hypothesize that the shift of the meridional wind from off-shore to on-shore direction during the BSBW translation through the Barents and northern Kara seas results in longer surface residence time for the BSBW sampled in 2006 compared with samples from 2005. The cooler, more saline, and better-ventilated BSBW sampled in 2006 may result from longer upstream translation through the Barents and northern Kara seas where the BSBW was modified by sea-ice formation and interaction with atmosphere. The data for stable oxygen isotopes from 1995 and 2006 reveals amplified brine modification of the BSBW core sampled downstream in 2006, which supports the assumption of an increased upstream residence time as indicated by wind patterns and dissolved oxygen values.
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  • 52
    Publication Date: 2019-09-23
    Description: Vodyanitskii mud volcano is located at a depth of about 2070 m in the Sorokin Trough, Black sea. It is a 500-m wide and 20-m high cone surrounded by a depression, which is typical of many mud volcanoes in the Black Sea. 75 kHz sidescan sonar show different generations of mud flows that include mud breccia, authigenic carbonates, and gas hydrates that were sampled by gravity coring. The fluids that flow through or erupt with the mud are enriched in chloride (up to similar to 650 mmol L-1 at similar to 150-cm sediment depth) suggesting a deep source, which is similar to the fluids of the close-by Dvurechenskii mud volcano. Direct observation with the remotely operated vehicle QUEST revealed gas bubbles emanating at two distinct sites at the crest of the mud volcano, which confirms earlier observations of bubble-induced hydroacoustic anomalies in echosounder records. The sediments at the main bubble emission site show a thermal anomaly with temperatures at similar to 60 cm sediment depth that were 0.9 degrees C warmer than the bottom water. Chemical and isotopic analyses of the emanated gas revealed that it consisted primarily of methane (99.8%) and was of microbial origin (delta D-CH4 = -170.8 parts per thousand (SMOW), delta C-13-CH4 = -61.0 parts per thousand (V-PDB), delta C-13-C2H6 = -44.0 parts per thousand (V-PDB)). The gas flux was estimated using the video observations of the ROV. Assuming that the flux is constant with time, about 0.9 +/- 0.5 x 106 mol of methane is released every year. This value is of the same order-of-magnitude as reported fluxes of dissolved methane released with pore water at other mud volcanoes. This suggests that bubble emanation is a significant pathway transporting methane from the sediments into the water column. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 53
    Publication Date: 2019-09-23
    Description: Anthropogenic CO2 emissions lead to chronically elevated seawater CO2 partial pressures (hypercapnia). The induced ocean acidification will very likely be a relevant factor shaping future marine environments. CO2 exposure concomitantly challenges the animal's capacity of acid-base and ionic regulation as well as the ability to maintain energy metabolism and calcification. Under conditions of acute hypercapnia, numerous studies have revealed a broad range of tolerance levels displayed by various marine taxa. Thus, it is well known that, in contrast to many marine invertebrates, most teleost fish are able to fully compensate acid-base disturbances in short-term experiments (hours to several days). in order to determine whether marine fish are able to preserve aerobic scope following long-term incubation to elevated CO2, we exposed two groups of Atlantic Cod for 4 and 12 months to 0.3 and 0.6 kPa P-CO2, respectively. Measurements of standard and active metabolic rates, critical swimming speeds and aerobic scope of long-term incubated cod showed no deviations from control values, indicating that locomotory performance is not compromised by the different levels of chronic hypercapnia. While the maintenance of high activity levels is supported by a 2-fold increased Na+/K+-ATPase protein expression and 2-fold elevated Na+/K+-ATPase activity in the 12 month incubated fish (0.6 kPa P-CO2), no such elevation in Na+/K+-ATPase activity could be observed in the group treated with 0.3 kPa P-CO2. Owing to the relevance of Na+/K+-ATPase as a general indicator for ion regulatory capacity, these results point at an adjustment of enzymatic activity to cope with the CO2 induced acid-base load at 0.6 kPa P-CO2 while under milder hypercapnic conditions the 'standard' Na+/K+-ATPase capacity might still be sufficient to maintain acid-base status. (c) 2009 Elsevier B.V. All rights reserved.
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  • 54
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    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 372 . pp. 75-81.
    Publication Date: 2017-07-11
    Description: The small sepiolid cephalopod Rossia moelleri Steenstrup, 1856 transfers sperm by implantation of spermatangia into female tissue. Although this is a common sperm transfer and storage strategy in cephalopods, the mechanism behind implantation of spermatangia is poorly understood. In the lab, we artificially induced the spermatophoric reaction and spermatangia implanted into female tissue. The force necessary to penetrate the mantle was measured using a needle attached to a force transducer. Taking diameter and bluntness factor into account, this force was estimated to be 0.3 N. Analysis of the spermatophoric reaction showed that the maximum force (1.12 μN–9.36 μN) produced as a result of acceleration (1.57–3.59 mm/s2) of the forward moving sperm mass (2.6–7 mg) was insufficient to be solely responsible for the penetration of the spermatangia into tissue. Scanning electron microscopy revealed no structures that could have facilitated the implantation of the spermatangium. Histological sections of the implanted spermatangium visualized the cement body being orally secreted from the spermatangium, probably facilitating the implantation either by lysis of the surrounding tissue or by acting as a lubricant during implantation. This study shows that the autonomous implantation process of spermatangia of R. moelleri does not have a purely mechanical basis but necessitates an additional, probably chemical mechanism or a combination of these two.
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  • 55
    Publication Date: 2017-08-22
    Description: The dissolution of in-situ generated methane hydrate in undersaturated, synthetic seawater (S = 35) was investigated in a series of laboratory-based experiments at P-/T-conditions within the hydrate stability field. A controlled flow field was generated across the smooth hydrate surface to test if, in addition to thermodynamic variables, the dissolution rate is influenced by changing hydrodynamic conditions. The dissolution rate was found to be strongly dependent on the friction velocity, showing that hydrate dissolution in undersaturated seawater is a diffusion-controlled process. The experimental data was used to obtain diffusional mass transfer coefficients kd, which were found to correlate linearly with the friction velocity, u★. The resulting kd/u★-correlation allows predicting the flux of methane from natural gas hydrate exposures at the sediment/seawater interface into the bulk water for a variety of natural P, T and flow conditions. It also is a tool for estimating the rate of hydrate regrowth at locations where natural hydrate outcrops at the seafloor persist in contact with undersaturated seawater
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  • 56
    facet.materialart.
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    Elsevier
    In:  Marine and Petroleum Geology, 26 . pp. 795-804.
    Publication Date: 2017-09-13
    Description: Heat flow anomalies provide critical information in active tectonic environments. The Gulf of Cadiz and adjacent areas are affected by the plate convergence between Africa and Europe, causing widespread deformation and faulting. Active thrust faults cause lateral movement and advection of heat that produces systematic variations in surface heat flow. In December 2003 new heat flow data were collected during the research vessel Sonne cruise SO175 in the Gulf of Cadiz over two sites of recent focused research activity: (i) the Gulf of Cadiz sedimentary prism and (ii) the Marques de Pombal escarpment. Both features have also been discussed as potential source areas of the Great Lisbon earthquake and tsunami of 1755. Background heat flow at the eastern terminus of the Horseshoe abyssal plain is about 52–59 mW/m2. Over the Gulf of Cadiz prism, heat flow decreases from ∼57 mW/m2 to unusually low values of 45 mW/m2 roughly 120 km eastward. Such low values and the heat flow trend are typical for active thrusting, supporting the idea of an east-dipping thrust fault. Slip rates are 10 ± 5 mm per year, assuming that the fault dips at 2°. A fault dipping at 5°, however, would result into slip rates of 1.5–5 mm per year, suggesting that subduction has largely ceased. Based on seismic data, the Marques de Pombal fault is interpreted as part of an active fault system located ∼100 km westward of Cape San Vincente. Heat flow over the fault is affected by refraction of heat caused by the 1 km high escarpment. Thermal models suggest that the slip rate along the fault must either be small or shear stresses acting on the fault are rather high. With respect to other fault zones, however, it is reasonable to assume that the fault's slip rate is small.
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  • 57
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    Elsevier
    In:  Deep-Sea Research Part II-Topical Studies in Oceanography, 56 . pp. 1868-1983.
    Publication Date: 2016-10-13
    Description: Analysis of the temporal and spatial variability of biological processes and identification of the main variables that drive the dynamic regime of marine ecosystems is complex. Correlation between physical variables and long-term changes in ecosystems has routinely been identified, but the specific mechanisms involved remain often unclear. Reasons for this could be various: the ecosystem can be very sensitive to the seasonal timing of the anomalous physical forcing; the ecosystem can be contemporaneously influenced by many physical variables and the ecosystem can generate intrinsic variability on climate time scales. Marine ecosystems are influenced by a variety of physical factors, e.g., light, temperature, transport, turbulence. Temperature has a fundamental forcing function in biology, with direct influences on rate processes of organisms and on the distribution of mobile species that have preferred temperature ranges. Light and transport also affect the physiology and distribution of marine organisms. Small-scale turbulence determines encounter between larval fish and their prey and additionally influences the probability of successful pursuit and ingestion. The impact of physical forcing variations on biological processes is studied through long-term observations, process studies, laboratory experiments, retrospective analysis of existing data sets and modelling. This manuscript reviews the diversity of physical influences on biological processes, marine organisms and ecosystems and their variety of responses to physical forcing with special emphasis on the dynamics of zooplankton and fish stocks.
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  • 58
    Publication Date: 2017-09-27
    Description: We present the first comprehensive set of dissolved 10Be and 9Be concentrations in surface waters and vertical profiles of all major sub-basins of the Arctic Ocean, which are complemented by data from the major Arctic rivers Mackenzie, Lena, Yenisey and Ob. The results show that 10Be and 9Be concentrations in waters below 150 m depth are low and only vary within a factor of 2 throughout the Arctic Basin (350–750 atoms/g and 9–15 pmol/kg, respectively). In marked contrast, Be isotope compositions in the upper 150 m are highly variable and show systematic variations. Cosmogenic 10Be concentrations range from 150 to 1000 atoms/g and concentrations of terrigenous 9Be range from 7 to 65 pmol/kg, resulting in 10Be/9Be ratios (atom/atom) between 0.5 and 14 × 10−8. Inflowing Atlantic water masses in the Eurasian Basin are characterized by a 10Be/9Be signature of 7 × 10−8. The inflow of Pacific water masses across the Bering Strait is characterized by lower ratios of 2–3 × 10−8, which can be traced into the central Arctic Ocean, possibly as far as the Fram Strait. A comparison of the high dissolved surface 10Be and 9Be concentrations (corresponding to low 10Be/9Be signatures of ∼2 × 10−8) in the Eurasian Basin with hydrographic parameters and river data documents efficient and rapid transport of Be with Siberian river waters across the Siberian Arctic shelves into the central Arctic Basin, although significant loss and exchange of Be on the shelves occurs. In contrast, fresh surface waters from the Canada Basin also show high cosmogenic 10Be contents, but are not enriched in terrigenous 9Be (resulting in high 10Be/9Be signatures of up to 14 × 10−8). This is explained by a combination of efficient scavenging of Be in the Mackenzie River estuary and the shelves and additional supply of cosmogenic 10Be via atmospheric fallout and melting of old sea ice. The residence time of Be in the deep Arctic Ocean estimated from our data is 800 years and thus similar to the average Be residence time in the global ocean.
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  • 59
    Publication Date: 2017-12-12
    Description: The potential of solid waste originating from a recirculated fish culture system, i.e faecal material, uneaten food pellets and bacterial biofilms was examined as food source for the marine polychaete Nereis diversicolor. These polychaetes could be a valuable food for fish if they provide essential fatty acids to the fish. Therefore, we analysed the fatty acid profiles from feed and faecal materials, the sediment as well as the cultured organisms - fish and several batches of N diversicolor - from an integrated recirculating aquaculture system. The major fatty acids (saturated, monounsaturated and polyunsaturated) for all analysed fish feed, fish and faeces samples were C16:0, C18:1 and C22:6 (n - 3), accounting for 48% to 57% of the fatty acids in the samples. The major fatty acids within the sediment were C16:0. C18:1 and C18:3 (n - 3). accounting for 61% of the total fatty acids. The samples of N. diversicolor revealed C16:0. C18:1 and C20:5 (n - 3) as the major fatty acids. Combined, they accounted for 56% of the total fatty acids detected within the worm samples. The results indicate that a recycling or even an upgrade of excreted feed nutrients such as fatty acids, which were otherwise discharged, can be achieved through integrated aquaculture combining fish and worm culture. (C) 2009 Elsevier B.V. All rights reserved.
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  • 60
    Publication Date: 2017-01-23
    Description: The intensification of the Northern Hemisphere Glaciation (INHG) was a major event in the development of the current climate state, and as one of the most productive regions in the world's oceans, the behaviour of the Benguela Upwelling System (BUS) following the INHG is of wide interest. To investigate post-INHG changes in productivity and organic matter accumulation, total organic carbon and biomarker accumulation rates were determined for sediments from COP Site 1083 and compared to alkenone-derived sea surface temperatures and nitrogen isotopic compositions. These data indicate that the interval between 2.6 and 2.4 Ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern BUS. The upwelling is reflected by significant changes in alkenone-derived SST estimates between glacial and interglacial intervals, with a total variability of 16 degrees C. The studied interval is also characterized by large changes in organic matter export as reflected by changes in TOC and biomarker accumulation rates, which show maxima during OIS 98 and during the transition from OIS 97 to 96. Intervals of elevated TOC are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower %CaCO(3), suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released CO(2) being consumed by CaCO(3) dissolution. However, in apparent contrast to recent Pleistocene sediments at the same site, organic matter export after the INHG was not solely driven by upwelling intensity. Of the three Pliocene glacial-interglacial cycles examined (OIS 101 to 96). each is unique with respect to the timing and magnitude of changes in organic matter accumulation. Each is also characterized by different algal assemblages as inferred from biomarker distributions, with OIS 97 and 96 particularly dominated by diatoms. We suggest that these differences reflect the important but evolving role of Southern Ocean waters in the Pliocene BUS: nutrient depletion of SO waters occurred during parts of Pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates. (C) 2009 Elsevier B.V. All rights reserved.
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  • 61
    Publication Date: 2019-08-07
    Description: There is an increasing concern over the safety of engineered nanoparticles (ENPs) to humans and the environment and it is likely that the environmental risks of these particles will have to be tested under regulatory schemes such as REACH. Due to their unique properties and the fact that their detection and characterisation in complex matrices is challenging, existing analytical methods and test approaches for assessing environmental risk may not be appropriate for ENPs. In this article we discuss the challenges associated with the testing of ENPs to generate data on persistence, mobility, bioavailability and ecotoxicity in the environment. It is essential that careful consideration is given to the selection of the test material, the test system (including test vessels and study media) and the test exposure conditions. During a study it is critical that not only the concentration of the ENP is determined but also its characteristics (e.g. size, shape, degree of aggregation and dissolution). A range of analytical techniques is available including microscopy-based approaches (e.g transmission and scanning electron microscopy), dynamic light scattering, and size separation approaches (e.g. field flow fractionation and hydrodynamic chromatography) coupled to detection methods such as inductively coupled plasma MS. All of these have their disadvantages: some are unable to distinguish between ENPs and natural interferences; some techniques require sample preparation approaches that can introduce artefacts; and others are complex and time-consuming. A combination of techniques is therefore needed. Our knowledge in this area is still limited, and co-ordinated research is required to gain a better understanding of the factors and processes affecting ENP fate and effects in the environment as well as to develop more usable, robust and sensitive methods for characterisation and detection of ENPs in environmental systems.
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  • 62
    Publication Date: 2017-09-27
    Description: This study establishes for the first time the chronology and limnological history of Lake Amora (Dead Sea basin, Israel), whose deposits (the Amora Formation) comprise one of the longest exposed lacustrine records of the Pleistocene time. The Amora Formation consists of sequences of laminated primary aragonite and silty-detritus, Ca-sulfate minerals, halite and elastic units. This sedimentary sequence was uplifted and tilted by the rising Sedom salt diapir, exposing similar to 320 m of sediments on the eastern flanks of Mt. Sedom (the Arubotaim Cave (AC) section). The chronology of the AC section is based on U-disequilibrium dating ((230)Th-(234)U and (234)U-(238)U ages) combined with floating delta(18)O stratigraphy and paleomagnetic constraints. The determination of the (230)Th-(234)U ages required significant corrections to account for detrital Th and U. These corrections were performed on individual samples and on suites of samples from several stratigraphic horizons. The most reliable corrected ages were used to construct an age-elevation model that was further tuned to the oxygen isotope record of east Mediterranean foraminifers (based on the long-term similarity between the sea and lake oxygen isotope archives). The combined U-series-delta(18)O age-elevation model indicates that the (exposed) Amora sequence was deposited between similar to 740 and 70 ka, covering seven glacial-interglacial cycles (Marine Isotope Stages (MI5) 18 to 5). Taking the last glacial Lake Lisan and the Holocene Dead Sea lacustrine systems as analogs of the depositional-limnological environment of Lake Amora, the latter oscillated between wet (glacial) and more arid (interglacial) conditions, represented by sequences of primary evaporites (aragonite and gypsum that require enhanced supply of freshwater to the lakes) and elastic sediments, respectively. The lake evolved from a stage of rapid shifts between high and low-stand conditions during similar to 740 to 550 ka to a sabkha-like environment that existed (at the AC site) between 550 and 420 ka. This stage was terminated by a dry spell represented by massive halite deposition at 420 ka (MIS12-11). During MIS10-6 the lake fluctuated between lower and higher stands reaching its highest stand conditions at the late glacial MIS6, after which a significant lake level decline corresponds to the transition to the last interglacial (MISS) low-stand lake, represented by the uppermost part of the Formation. delta(18)O values in the primary aragonite range between 6.0 and -1.3 parts per thousand, shifting cyclically between glacial and interglacial intervals. The lowest 8180 values are observed during interglacial stages and may reflect short and intense humid episodes that intermittently interrupted the overall arid conditions. These humid episodes, expressed also by enhanced deposition of travertines and speleothems, seem to characterize the Negev Desert, and in contrast to the overall dominance of the Atlantic-Mediterranean system of rain patterns in the Dead Sea basin, some humid episodes during interglacials may be traced, to southern sources. (C) 2009 Elsevier Ltd. All rights reserved.
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  • 63
    Publication Date: 2014-10-02
    Description: Trypanosomiasis and leishmaniasis pose major public health threats for many countries, particularly those in sub-Saharan Africa and South America. In the present study, we evaluated the in vitro antiprotozoal activity of three irregular, linear sesquiterpene lactones recently isolated from Greek Anthemis auriculata, namely anthecotulide (1), 4-hydroxyanthecotulide (2) and 4-acetoxyanthecotulide (3). Trypomastigote forms of Trypanosoma brucei rhodesiense and T. cruzi as well as axenic amastigotes of Leishmania donovani were used for testing. The cytotoxic potential of the compounds was also assessed against mammalian (rat) skeletal myoblasts (L6 cells). All compounds showed potent trypanocidal and leishmanicidal activity. 4-Hydroxyanthecotulide (2) appeared to be the most active compound against all parasites, particularly towards T. b. rhodesiense (IC50 0.56 μg/ml), whereas 4-acetoxyanthecotulide (3) was the least active. All three metabolites possessed toxicity on mammalian cells, which might limit their use as antiprotozoal agents.
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  • 64
    Publication Date: 2015-01-27
    Description: The Gulf of Cadiz, off SW Iberia and the NW Moroccan margin, straddles the cryptic plate boundary between Africa and Eurasia, a region where the orogenic Alpine compressive deformation in the continental collision zone passes laterally to the west to strike-slip deformation. A set of new multibeam bathymetry, multi-channel and single-channel seismic data presented here image the main morphological features of tectonic origin of a significant part of the Gulf of Cadiz from the continental shelf to the abyssal plain. These morphotectonic features are shown to result from the reactivation of deeply rooted faults that changed their kinematics from the early Mesozoic rifting, through the Late Cretaceous–Paleogene collision, to the Pliocene–Quaternary thrusting and wrenching. The old faults control deep incised, more than 100 km long canyons and valleys. Several effects of neotectonics on deep water seabed are shown. These include: i) the complex morphology caused by wrenching on the 230 km long WNW–ESE faults that produced en echelon folds on the sediments; ii) the formation of up to 5 km wide crescent shaped scours at roughly 4 km water depth by reactivation of thrusts; iii) 10 km long creep folds on the continental slope; and iv) the formation of landslides on active fault escarpments. The present day deformation is partitioned on NE–SW thrusts and WNW–ESE to W–E strike-slip faults and is propagating northwards on N–S trending thrusts along the West Iberia Margin from 35.5°N to 38°N, which should be considered for seismic hazard.
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  • 65
    Publication Date: 2015-01-27
    Description: New high-resolution multi-beam bathymetry data allowed the recognition of several bathymetric lineaments (ca. 100 km long, trending WNW–ESE) in seafloor sediments of the Gulf of Cadiz, offshore SW Iberia. The interpretation of multi-channel (MCS) profiles crosscutting these lineaments showed that they are controlled by underlying deep seated faults, which have endured a polyphase reactivation history. To get insights on the Recent tectonic evolution of these structures, we performed two sets of analogue modelling experiments, assuming: 1) right-lateral strike-slip basement faulting and coupled passive shearing affecting an overlying soft cover; and 2) low-angle transpressive deformation along a narrow shear band overlying the fault. Our results show a good correlation between the experimentally obtained structural patterns and the natural morphotectonic lineaments, allowing the use of some of the observed natural features as strain gauges. Based on this, we conclude that the study lineaments correspond to the bathymetric expression of ongoing dextral wrenching reactivation of WNW–ESE pre-existing faults, and we estimate the age of this tectonic reactivation as being ca. 1.8 Ma (i.e. form late Pliocene to Present day). These characteristics agree with the most recent kinematic models derived from geodetic observations, indicating that Present day convergence between Nubia and Iberia is subparallel to the newly identified lineaments and occurs at a 4 mm/yr rate.
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  • 66
    Publication Date: 2019-12-31
    Description: The Quaternary history of Beringia and of the Arctic–Pacific marine connection via the Bering Strait is poorly understood because of the fragmentary stratigraphic record from this region. We report new borehole and seismic-reflection data collected in 2006 in the southwestern Chukchi Sea. Sediment samples were analyzed for magnetic properties, grain size, heavy minerals, and biostratigraphic proxies (spores and pollen, foraminifers, ostracodes, diatoms, and aquatic palynomorphs). Two shallow boreholes drilled between the Chukotka Peninsula and the Wrangel Island recovered sediments of two principal stratigraphic units with a distinct unconformity between them. Based on predominantly reverse paleomagnetic polarity of the lower unit and pollen spectra indicative of forested coasts and climate warmer than present, the age of this unit is estimated as Pliocene to early Pleistocene (broadly between ca. 5 and 2 Ma). Attendant sedimentary environments were likely alluvial to nearshore marine. These deposits can be correlated to the seismic unit infilling valleys incised into sedimentary bedrock across much of the study area, and possibly deposited during a transgression following the opening of the Bering Strait. The upper unit from both boreholes contains Holocene 14C ages and is clearly related to the last, postglacial transgression. Holocene sediments in Borehole 2 indicate fast deposition at the early stages of flooding (between ca. 11 and 9 ka) to very low deposition, possibly related to expansive sea ice. Closer to shore, deposition at Borehole 1 resumed much later (ca. 2 ka), likely due to a change in the pattern of coastal erosional processes and/or the demise of a landbridge between the Chukotka Peninsula and the Wrangel Island inferred from studies on mammoth distribution.
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  • 67
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    Elsevier
    In:  Current Opinion in Chemical Biology, 13 (2). pp. 205-215.
    Publication Date: 2018-11-05
    Description: The biosynthesis of the microbial small molecule iron scavengers known as siderophores has been of interest since their discovery in the middle of the past century. Two main pathways for siderophore biosynthesis exist. One is directed by a large family of modular multienzymes called non-ribosomal peptide synthetases (NRPSs) while the other is NRPS independent. There has been a vast increase in our knowledge of siderophore biosynthesis over the past two decades and the enzymology of several NRPS-dependent pathways is now well-understood while dramatic recent progress has also been made in elucidating NRPS-independent pathways. As siderophores are virulence factors in many pathogenic microorganisms, genetic and biochemical knowledge of siderophore biosynthetic pathways can aid in the development of new antimicrobials as well as increasing our understanding of the natural machinery for the efficient assembly of structurally complex bioactive natural products.
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  • 68
    Publication Date: 2019-12-31
    Description: Sea ice is an important climate variable and is also an obstacle for marine operations in polar regions. We have developed a small and lightweight, digitally operated frequency-domain electromagnetic-induction (EM) system, a so-called EM bird, dedicated for measurements of sea ice thickness. It is 3.5 m long and weighs only 105 kg, and can therefore easily be shipped to remote places and operated from icebreakers and small helicopters. Here, we describe the technical design of the bird operating at two frequencies of f1 = 3.68 kHz and f2 = 112 kHz, and study its technical performance. On average, noise amounts to ± 8.5 ppm and ± 17.5 ppm for f1 and f2, respectively. Electrical drift amounts to 200 ppm/h and 2000 ppm/h for f1 and f2, during the first 0.5 h of operation. It is reduced by 75% after 2 h. Calibration of the Inphase and Quadrature ppm signals varies by 2 to 3%. A sensitivity study shows that all these signal variations do affect the accuracy of the ice thickness retrieval, but that it remains better than ± 0.1 m over level ice in most cases. This accuracy is also confirmed by means of comparisons of the helicopter EM data with other thickness measurements. The paper also presents the ice thickness retrieval from single-component Inphase data of f1.
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  • 69
    Publication Date: 2015-08-06
    Description: The Middle Cambrian (~ 540 Ma) Gahcho Kué Kimberlite Field is situated about 275 km ENE of Yellowknife, NWT, Canada. The kimberlites were emplaced into 2.6 Ga Archean granitic rocks of the Yellowknife Supergroup. Four larger kimberlite bodies (5034, Tesla, Tuzo, and Hearne) as well as a number of smaller pipes and associated sheets occur in the field. In plan view, the Tuzo pipe has a circular outline at the surface, and it widens towards deeper levels. The pipe infill consists of several types of coherent and fragmental kimberlite facies. Coherent or apparent coherent (possibly welded) kimberlite facies dominate at depth, but also occur at shallow levels, as dikes intruded late in the eruptive sequence or individual coherent kimberlite clasts. The central and shallower portions of the pipe consist of several fragmental kimberlite varieties that are texturally classified as Tuffisitic Kimberlites. The definition, geometry and extent of the geological units are complex and zones controlled by vertical elements are most significant. The fluidal outlines of some of the coherent kimberlite clasts suggest that at least some are the product of disruption of magma that was in a semi-plastic state or even of welded material. Ragged clasts at low levels are inferred to form part of a complex peperite-like system that intrudes the base of the root zone. A variable, often high abundance of local wall-rock xenoliths between and within the kimberlite phases is observed, varying in size from sub-millimeter to several tens of meters. Wall-rock fragments are common at all locations within the pipe but are especially frequent in a domain with a belt-like geometry between 120 and 200 m depth in the pipe. Steeply outward-dipping bedded deposits made up of wall-rock fragments occur in deep levels of the pipe and are especially common under the downward-widening roof segments. The gradational contact relationships of these deposits with the surrounding kimberlite-bearing rocks as well as their location suggest that they formed more-or-less in situ. Different breccia facies inside the pipe suggest an origin by slumping, grain flows, rock fall or pyroclastic deposition. The shape and facies architecture of the Tuzo pipe suggests that the studied section of the pipe lies at a root zone–diatreme transitional structural level. Composite coherent kimberlite clasts imply that recycling processes were active over time, while reworked wall-rock rich deposits and ductily-deformed clasts of welded kimberlite point to the presence of temporary cavities in the root zone. The emplacement of the Tuzo pipe did not occur in a single, violent explosion, but involved repetitive volcanic explosions alternating with periods of relative quiescence. The observed features are typical of phreatomagmatic processes, which may include phases of less-explosive magmatic activity.
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  • 70
    Publication Date: 2015-09-25
    Description: In July 2007, phosphorus input by an upwelling event along the east coast of Gotland Island and the response of filamentous cyanobacteria were studied to determine whether introduced phosphorus can intensify cyanobacterial bloom formation in the eastern Gotland Basin. Surface temperature, nutrient concentrations, phytoplankton biomass and its stoichiometry, as well as phosphate uptake rates were determined in two transects between the coasts of Gotland and Latvia and in a short grid offshore of Gotland. In the upwelling area, surface temperatures of 11–12 °C and average dissolved inorganic phosphorus (DIP) concentrations of 0.26 μM were measured. Outside the upwelling, surface temperatures were higher (15.5–16.6 °C) and DIP supplies in the upper 10 m layer were exhausted. Nitrite and nitrate concentrations (0.01–0.22 μM) were very low within and outside the upwelling region. Abundances of filamentous cyanobacteria were highly reduced in the upwelling area, accounting for only 1.4–6.0% of the total phytoplankton biomass, in contrast to 18–20% outside the upwelling. The C:P ratio of filamentous cyanobacteria varied between 32.8 and 310 in the upwelling region, most likely due to the introduction of phosphorus-depleted organisms into the upwelling water. These organisms accumulate DIP in upwelling water and have lower C:P ratios as long as they remain in DIP-rich water. Thus, diazotrophic cyanobacteria benefit from phosphorus input directly in the upwelling region. Outside the upwelling region, the C:P ratios of filamentous cyanobacteria varied widely, between 240 and 463, whereas those of particulate material in the water ranged only between 96 and 224. To reduce their C:P ratio from 300 to 35, cyanobacteria in the upwelling region had to take up 0.05 mmol m−3 DIP, which is about 20% of the available DIP. Thus, a larger biomass of filamentous cyanobacteria may be able to benefit from a given DIP input. As determined from the DIP uptake rates measured in upwelling cells, the time needed to reduce the C:P ratio from 300 to 35 was too long to explain the huge bloom formations that typically occur in summer. However, phosphorus uptake rates increased significantly with increasing C:P ratios, allowing phosphorus accumulation within 4–5 days, a span of time suitable for bloom formation in July and August.